The present invention relates to a method for fabricating a composite material out of a parent substance containing silicon nitride and a metal silicide, through gas pressure sintering in a nitrogenous atmosphere and a silicon-containing composite material, whose silicon-containing constituents are made of Si3N4 and of a metal silicide.
There are composite materials, which contain silicon nitride and metal silicide, and methods for their preparation. The fabrication of such materials through single-axial not pressing (unconfined sintering under pressure) is discussed in German Published Patent Application Nos. 37 34 274 and 36 06 403, in which the parent substance contains Si3 N4 and the metal silicide MoSi2, and in European Patent Application No. 0 335 382, in which the parent substance contains Si3 N4 and MO5 Si3 as the metal silicide and carbon, and the fabricated material contains as metal silicide, Mo5Si3C or, more precisely, Mo5xe2x88x92XSi3C1xe2x88x92Y (0xe2x89xa6Xxe2x89xa62; 0xe2x89xa6Yxe2x89xa61). The electrical properties of the materials fabricated in this manner are able to be selectively adjustable. It is believed that the method is industrial and requires considerable outlay for energy consumption and that the application of the method only permits fabrication of complex geometrical structures in expensive, hard-machining operations.
German Published Patent Application No. 195 00 832, i.e., European Patent Application No. 0 721 925, discusses the fabrication of highly heat-resistant silicon nitride composite materials, which contain a reinforcement component of Me5Si3 and, moreover, MeSi2 or MeSi2, and silicides of other stoichiometries, Me standing for metal. Mixed into the parent substance as metal silicide are MeSi2 and Me5Si3, or only MeSi2. The metals may be selected from the group including molybdenum, tungsten, chromium, tantalum, niobium, manganese and vanadium. The sintering is performed as gas pressure sintering (at N2 pressures of 100 bar), which makes it possible to fabricate molded articles (shaped bodies), virtually with their final contours, in ceramic injection molding or pressing processes, with subsequent green processing, or in hot-pressing (sintering under pressure) processes. Special electrical properties cannot be
An object of an exemplary embodiment of the present invention is an industrially simple and energy-saving method for fabricating composite materials containing silicon nitride and metal silicide and having fixed electrical properties, which makes it possible to manufacture the molded articles, virtually with their final contours, from the composite material, prior to the sintering operation, and to specify representatives of such composite materials in an exemplary method, where Me5 Si3 is introduced as the metal suicide into the parent substance, the partial pressure of the nitrogen being established as a function of the sintering temperature in such a way that, at the lower limit of the practical range, Si3N4 is still thermodynamically stable and, at the upper limit, Me5Si3, and is dissolved into a composite material of the type mentioned at the outset, the sit metal silicide being selected from the group Nb5Si3, V5Si3, Ta5Si3 and W5Si3.
To exploit the advantages of the gas-pressure sintering method, at the same time while manufacturing composite materials having fixed electrical properties it was ascertained that the electrical properties cannot be adjusted in a determinate fashion (definably) when N2 applied above a specific pressure range. During test trials, it was found that there is a range of the N 2 partial pressures within which one can prevent other silicon-containing components, besides Si3N4 and Me5Si3, from being present in the finished composite material. In this manner, composite materials were fabricated having fixed electrical properties. In comparison to the hot-pressing (sintering under pressure) method, the gas-pressure sintering method makes do with a much simpler sintering device. Compact, high-strength materials are able to be fabricated with the exemplary method to the present invention. In comparison to materials containing MeSi2, materials containing Me5Si3 are believed to a very low temperature dependency of the electrical conductivity.
The method is carried out in such a way that the metal silicide in the composite material has a carbon concentration (preferably between about 0.3 and about 0.6% by weight specific to the composite material), i.e., is present as Me5Si3(C).